1. Field of Invention
The present invention relates to a car-navigation system and storage medium for determining an estimated position of a vehicle.
2. Description of Related Art
Conventionally, various methods have been proposed for judging whether a road where a vehicle is traveling is an expressway (expressway, metropolitan express, toll road, or the like) or other ordinary road. For example, a method, has been proposed (Japanese Patent Application No. HEI 3-154818) for judging that a vehicle may have passed a toll road if the vehicle speed is equal to or less than a predetermined value at the position of a toll gate obtained from map information, estimating the correlation of the vehicle with the toll road higher than that correlation with other roads and, thereupon, correcting the present position of the vehicle through the selection of a road, judging that there is little possibility the vehicle has passed a toll road if the vehicle speed does not lower to a predetermined value or less, estimating the correlation of the vehicle with the toll road lower than the correlation with the other roads, and thereupon, correcting the present position of the vehicle through the selection of a road.
On the other hand, a method has been proposed (Japanese Patent Application No. HEI 2-137096) in which time-keeping is started when a vehicle speed is determined to be equal to or higher than a predetermined speed, and it is determined that the vehicle is traveling on an expressway if the time is equal to or more than a predetermined time. In short, a vehicle is determined to be traveling on an expressway when a traveling speed equal to or higher than a predetermined speed has been sustained for a predetermined time or longer.
In addition, a method has been proposed (Japanese Patent No. 3027574) for distinguishing the upper layer where the ratio of sections that are GPS positioned in a certain sectional distance is equal to or more than a certain upper layer distinction threshold, for the travel of one""s vehicle on a multilayer road, and distinguishing the lower layer in case where the ratio is equal to or less than a certain lower layer distinction threshold.
Moreover, a method for receiving an electric wave from the GPS satellite, and distinguishing a road to be an ordinary road if the angle of elevation of the GPS satellite is equal to or less than a predetermined angle, and an upper layer of an elevated road if the angle of elevation of the GPS satellite is greater than the predetermined angle, has been proposed (Japanese Patent Application No. HEI 10-141968).
In the method for distinguishing whether the vehicle has passed a toll road or not according to whether the vehicle speed at the position of a toll gate is equal to or less than a predetermined value, the vehicle speed may happen to be equal to or less than the predetermined value even when the vehicle is traveling on an ordinary road, particularly where a traffic light is red, because there are places where traffic lights exist near the toll gate given the actual traffic situation. In such places, the road on which a vehicle is traveling can not be judged by the toll gate and the vehicle speed.
In the method wherein the vehicle is judged to be traveling on an expressway if it is distinguished that the time for traveling at or more than the predetermined speed is equal to or more than the predetermined time, it is impossible to judge whether a vehicle is traveling on an expressway or not simply by the vehicle speed, because there are cases where the vehicle speed is considerably high even on ordinary, i.e., non-expressway, roads if such an ordinary road is, for example, a main arterial road, permitting a high vehicle speed limit or an expressway feeder road also having a high speed limit.
In the method for distinguishing the upper layer from the lower layer of a multi-layer road by the ratio of sections that are GPS positioned for traveling on the multilayer road, it is impossible to judge whether the vehicle is traveling on an upper layer or not simply from the GPS positioning state, because there are cases where structures, such as a building or the like existing around the road, block the GPS electric wave rendering the GPS positioning ineffective in these places.
Further, in the method for distinguishing an ordinary road from an upper layer of an elevated road depending on whether the angle of elevation of the received GPS satellite is equal to or less than a predetermined angle, places exist where there is no upper layer portion of the elevated road over the ordinary road for some lanes, and electric wave signals from the GPS satellite are not blocked. In such places, it is impossible to distinguish the upper layer from the lower layer of the elevated road based on the angle of elevation of the GPS satellite signal.
The invention has been devised to solve the aforementioned problems, and it is an object of the invention to determine the estimated position of a vehicle accurately even under various situations.
The invention provides a car-navigation system for determining the estimated position of a vehicle, characterized by comprising reception means for receiving electric wave signals from a plurality of positioning satellites, vehicle speed detection means for detecting the speed of a vehicle, storage means for storing at least received positioning satellite information and detected vehicle speed information, and control means for judging whether the vehicle has passed a tollgate based on the positioning satellite information and the vehicle speed information stored in the storage means.
The invention also provides a car-navigation system for judging the upper and lower roads of a multilayer road, characterized in that comparison coefficients are allocated to a plurality of judgment conditions, and the upper and lower roads of the multilayer road is judged based on the sum of comparison coefficients.
The invention also provides a car-navigation system for determining the estimated position of a vehicle, characterized by comprising reception means for receiving electric wave signals from a plurality of positioning satellites, and control means for allocating comparison coefficients based on an angle of elevation of the received satellite, and judging the estimated position of a vehicle based on the sum of the comparison coefficients.
The invention further provides a car-navigation system for determining the estimated position of a vehicle, characterized by comprising a first judgment means for judging whether the expressway is predominant as the estimated position, a second judgment means for judging whether the ordinary road is predominant as the estimated position, and control means for determining the vehicle estimated position based on the judgment results of the first and second judgment means.
Further still, the present invention provides a storage medium having a built-in program for determining an estimated position of a vehicle, characterized by comprising a first judgment for judging whether the expressway is predominant as the estimated position, a second judgment for judging whether the ordinary road is predominant as the estimated position, and a built-in program for determining the vehicle estimated position based on the judgment results of the first and second judgments.